Naguabo is a municipal area in Puerto Rico that is part of the eastern coastal valley region.  Home to 26,720 people as of the 2010 U.S. Census, Naguabo’s economy primarily consists of agriculture, raising livestock, fishing, and manufacturing.  Naguabo’s many rivers and streams carry down fertile soil from the mountains. Part of the municipality is in the Luquillo Mountain Range and contains the scenic El Yunque National Forest, while the rest of the territory is flat. 
Hurricane Maria first made landfall in Humacao, just south of Naguabo. These areas, along with others along the eastern coast, faced much destruction yet had power restored much later than the rest of the island. Many people in Naguabo went eight or more months without electricity, and even a year after the storm, lights went out for hours at a time and some families still lacked running water. Naguabo has traditionally been an underserved area in Puerto Rico, and Hurricane Maria has only exacerbated residents’ economic and general insecurity. Many have had to spend their savings powering backup generators for months. This loss of routine and purpose may be connected to a simultaneous increase in hopelessness, suicide attempts, and suicide fatalities. 
Because it took so long for Naguabo to get its power back, it could benefit from microgrid technology. As seen in Figure 1, Puerto Rico’s electrical grid is largely centralized and relies on long transmission lines to carry energy from a few fossil fuel-burning plants.  However, a microgrid is locally-based and uses a system of controls that allows it to disconnect from the main grid when problems occur and still supply energy to critical loads like hospitals and community centers. Thus, a microgrid allows a community’s electric grid to function as an island and not rely so much on the main grid (S&C Electric Company, 2019).
Calculations and Assumptions
In fiscal year 2014, the total energy consumption for Naguabo was 5000 MWh.  Dividing annual consumption by the number of hours in a year gives an average demand of 0.571 MW.
However, there will be times when energy use may significantly exceed this average (for example, there might be an abnormally warm day that causes a surge in air conditioning use). Thus, we multiply the average by 2 to estimate what the peak demand may be, giving 1.142 MW.
In addition, when electricity travels from the power plant to people’s homes via transmission lines, some of the energy is lost as heat. Puerto Rico’s transmission and distribution losses were calculated to be 13.8% by the National Renewable Energy Laboratory. This means that the grid must be able to support at least 13.8% more than the estimated peak demand, or approximately 1.299 MW.
Finally, since the world’s energy consumption is generally increasing, we considered load growth in our calculation. However, the 2019 PREPA Integrated Resource Plan predicts a 0.23% per year decline in energy demand through 2038 because of the decreasing population and softening GNP growth after 2027.  The population estimate for Naguabo as of 2018 had decreased to 25,376, indicating that we can apply this island-wide assumption to Naguabo.  As a result, we believe that the grid will not need to support more than the estimate of 1.299 MW since demand is expected to decrease over time.
Based on these calculations, any energy system established in Puerto Rico should be equipped to provide 1.299 MW of power at any given time.
Generation of Electricity
The first thing any power grid needs is a means to generate energy. We believe Naguabo should implement solar power as the primary energy source for the microgrid, and recommend that hydroelectric power also be further investigated.
As seen in Figure 2, Naguabo has high photovoltaic power potential and can capitalize on this opportunity by using solar power to meet its energy needs. Naguabo averages 5.65 kWh/m2/day of solar potential, and this number climbs during the early spring and late summer.  A combination of rooftop solar and a 1-MW solar array could be used to generate most of the 1.299 MW. However, since the production of solar energy is unpredictable and may not align with times that people use the most power, different forms of energy storage should be considered as well. For example, Naguabo could investigate gravitational potential energy as a form of storage, as well as other forms, so that power is available in case of a cloudy day or during the nighttime. As energy storage technologies continue to develop, becoming more reliable and accessible, we propose that Naguabo integrate these into its power system.
Since Naguabo is home to many rivers, hydropower is a good resource that may be considered as well. Hydropower has the additional benefits of being more reliable than solar and not requiring batteries to store energy. In particular, pumped hydro, which involves moving water from a lower body to a higher body to store it as potential energy, already stores 22 GW in the U.S. grid.  However, further water flow and environmental analyses should be conducted to see if this is feasible. 
Naguabo is home to the 23.4-MW Punta Lima Wind Farm, but it has been left inoperational due to Hurricane Maria. Thus, it is not being considered as a source of energy for this proposal, since hydropower has been more resilient during hurricanes in the past.  In addition, Naguabo’s proximity to the sea opens ideas for ocean energy, but the technology for ocean energy is much further behind that of other renewables. As a result, we believe that solar and hydropower will be most reliable and cost-effective for Naguabo to meet its energy needs. 
According to a study conducted by the National Renewable Energy Laboratory (NREL), the average cost to build a community-scale microgrid in the United States was $2,119,908 per MW. These costs include generation of power, establishing energy storage, developing a control system, building additional infrastructure, and covering other “soft costs” such as engineering, commissioning, and regulations. 
If Naguabo wanted to meet its entire 5000 MWh energy demand using solar, then estimates by NREL say that a solar array of at least 3.3 MW could meet this need.  First Solar, a top U.S. photovoltaic manufacturer, has estimated that the cost per watt of a community-scale solar farm is about $1/Watt.  Thus, we estimate that a 3.3 MW solar farm would cost around $3.3 million.
For hydropower, Naguabo has an advantage in that it is already home to the Rio Blanco Dam. Although this dam does not produce electricity, it is possible to retrofit it with hydropower capabilities. This has been done with other dams in the continental U.S. and is cheaper than having to build a dam from scratch. For example, the Red Rock Dam in Iowa was built in 1969 and cost $88 million, which is about $617 million in today’s currency. However, it is currently being retrofitted with hydroelectric capabilities, and this project is expected to cost $380 million.  The Rio Blanco Dam is smaller than the Red Rock Dam, so retrofitting it may not cost as much. In addition, the hydroelectric power generated by the dam would be more reliable than solar or wind and would provide a way to store energy without using expensive batteries or other devices.
Applications to Other Cities
Although this case study is specific to Naguabo, other cities could follow a similar process to create their own energy plans. They would first need data on total energy consumption. We used data readily available from the Puerto Rico Energy Bureau, but municipalities may keep their own data that is more accurate and up-to-date. Once they have a baseline consumption, they can make a few assumptions about peak demand, transmission losses, and load growth. The peak demand and transmission loss factors could be kept the same, but municipalities will need to look at their own population and energy use trends to determine if their load is growing. The trend across the whole island is that energy demand is decreasing because of population loss, and this was true for Naguabo. However, that may not be true in every city. Finally, with this final target number, the city could look at its existing resources and try to calculate a way to meet this energy demand. Naguabo gets plenty of sunlight and has many rivers, so we have recommended solar and hydropower; other regions may have different resources available.